Method of storing volatile liquids



June 24, 1952 Q J, MERRIAM 2,601,313

s METHOD OF STORING VOLATILE LIQUIDS Filed Nov. 13, 1945 lPatented June 24, 1952 METHOD OF STORING VOLATILE LIQUIDS Charles J. Merriam, Winnetka, Ill., assignor to Chicago Bridge & Iron Company, a corporation of Illinois Application November 13, 1945, Serial No. 628,239

6 Claims.

This invention relates to a method of operating a storage vessel, and particularly to a method of operating a storage vessel for liquid such as gasoline which has a substantial vapor pressure which is normally substantially below atmospheric pressure.

The problem of storing such a volatile liquid has been dealt with in the past in many Ways. When stored in ordinary vessels, there is no problem so long as the vessel is completely full. Upon emptying and refilling, however, there is evaporation into the vapor space. Normally the vapor space is left open to atmosphere so that air enters and is forced out carrying with it a substantial quantity of gasoline.

In order to overcome this diiliculty, a large number of mechanical expedients have been suggested, including floating roofs, breather roofs, lifter roofs, and the like. All of these present mechanical diiiculties and are expensive to opcrate.

The present invention permits the operation of a storage vessel with xed walls. In accordance with it, a storage vessel is made suiciently strong to withstand substantially full atmospheric pressure directed inwardly and to withstand an internal gauge pressure substantially equal to atmospheric. The vessel, when filled the rst time, is permitted to vent to atmosphere to remove substantially all air, and the tank is preferably lled to the top. After filling, about 2% of liquid is withdrawn to allow for expansion but no air is vented into the space thus vacated. Furthermore on removal of liquid from the vessel, no air is admitted thereto, liquid being removed by means of a pumping system capable of operating against full vacuum (or full vacuum less the vapor pressure of the liquid). On filling the vessel no venting is contemplated. However, venting may be required whenever the safety limit of the tank is exceeded. Normally such venting will not be required, but excessive pressure may be developed in three ways: (l) by excessively high temperatures; (2) too rapid filling; and 3) by reason of the additive vapor pressure of air entrapped or entrained in the liquid.

When the vessel is filled it is obvious that vapors therein will be compressed. Theoretically, these vapors will condense when they reach a pressure exceeding maximum vapor pressure, but this does not always follow immediately, and particularly is not necessarily true where the vessel is iilled with extreme rapidity and in the presence of air. Normally I prefer to ll the vessel in a manner so that pressure generated in the gasoline vapors Will remain low, the excess pressure generated by compression being taken up by condensation in the liquid.

It is of course impossible to remove all air entrapped or entrained by the liquid and, therefore,

air will accumulate slowly within the vessel. This air not only adds its vapor pressure to that of the gasoline vapors, but it interferes with the proper condensation of the gasoline during filling and ultimately requires removal. For this reason I provide a vent which operates at nearly the safety limit of the tank for removing excessive air. The air obviously carries with it vapor, the loss of which is undesirable. 'I'his loss is kept to a minimum by venting when the safety limit of the tank has been approximately reached, and may further be reduced by cooling or refrigerating the vented air in any suitable manner and returning condensate to the tank.

The use of a vent valve operating at the safety limit of the tank is not only important because venting is limited to the minimum, but because it insures that the concentration of air in the gas vapor will normally have been markedly increased prior to venting. This increase in concentration of air occurs for two reasons. In the first place the vapor pressure of the gasoline is xed at any temperature. Therefore, if the tank is set to vent at l2 lbs. and the vapor pressure of the gasoline is, say 5 lbs. absolute, air will have to represent approximately 22 lbs. of the total pressure before any venting occurs. Therefore, increase in pressure represents air, and the higher the pressure of venting, the greater is the proportion of air, other things being equal.

Furthermore, venting will nearly always occur during filling of the tank and seldom While the tank is quiescent. During lling of the tank, the pressure will rise, as any residual air is compressed, but at the same time gasoline vapors within the vapor space will condense because their condensation pressure is exceeded the minute the tank begins to fill. Therefore, the vapors gradually become more concentrated in air as the lling operation goes on, and by making the venting pressure as high as possible, the concentration of air increases and less gasoline vapors are lost upon venting.

It is preferred, as stated before, to ll the tank completely full whenever it is lled, and then to withdraw some liquid and leave about 2% of vapor space. This, however, is not customary reiinery practice, the ordinary practice being to iill about 98 full. In order to conform to this practice, it is, therefore, desirable in some instances to include a second valve which is sealed against operation until the tank is substantially 98% full, and then opens slightly below the safety limit of the tank and preferably at a pressure very slightly below the first valve, and which then stays open to vent all of the gases contained Within the 2 space until atmospheric pressure has been reached. Such a valve is of value because it vents gases at a time when the concentration of air therein is at a maximum. This maximum content of air is due to the fact that gasoline vapors have been condensing during all of the filling of the tank, the air concentration increasing during all of that time. By venting as much as possible when the air concentration is at its maximum, vapor losses are reduced.

A typical storage system for storing volatile liquids according to the method of this invention is shown in the accompanying drawings. Of the drawings Fig. 1 is an elevation of the storage system; and Fig. 2 is an enlarged fragmentaryrvertical section through the Valves on i the top of the storage Vessel.

The storage system shown in the accompanying drawings comprises a storage vessel I9, a pump I l avalve I2 set at adesired pressure such as 12 lb. perv sq. in., and a secondyalve i3 preferably set at a slightly lower pressure than the first valve IZ. The second Valve I3 is designed to open at, for example, 11% 1b. per sq. in., and to close at substantially atmospheric pressure.

The storage Vessel I comprises vertically aligned intersecting spheres I4 supported by a steelrim iwhich rests upon a concrete foundation iii. This intersecting spherical vessel is ci the type shown anddescribed in the copending application of Harry C. Boardman, Serial No. $08,884:, led August 4, 1945.

The i'irst valve i2 at the top of the storage vessel comprises a valve seat i6 held in closed position by a spring il resting. against cross bars i3. This valve maybe set at any desired pressure, such as l2 lb. per sq. in.

The second valve I3 at the top of the storage vessel includes a rst valve seat i9 connected by means of a rod 29 to a second valve seat EI of larger area than the first valve seat I9. Both valve seats are held in place by means of a spring 22 bracing against cross bars 23. The opening 25% leading to the second Valve I3 is normally kept closed by means cfa gate 25. This gate is opened only when the vessel is slightly less than full, for example, 98% full, and is opened by means of a iicat 25, which turns the gate 25 about hinge 2, when the vessel is'almcst filled.

rihe outlet from the Valves may be joined to a pipe 23, Where the vapors may be conducted to a reirigerating unit to recover the volatile liquid carried 01T by the vapors.

An important part of the storage system is a means for lling and emptying the vessel. This iilling and emptying means may be a pump II which must be of sunicient power to ll the vessel against internal pressure and to empty the tank against full vacuum (or full vacuum less the vapor pressure of the liquid). Liquid is led to the pump by means of an intake line 29 and eX- hausted to the vessel through a line 3G. When the pump is used towithdraw liquid from the vessel these lines lserve as an outlet.

Having described my invention in considerable detail, it is my intention that the invention be not limited by the details of description unless otherwise specified, but rather be construed .broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1. The method of iilling and emptying a storage vessel for storing volatile liquids having a substantial vapor pressure normally substantially below atmospheric pressure which comprises introducing such liquidto a storage vessel capable of withstanding substantially a full vacuum and also an internal gauge pressure substantially equal to atmospheric pressure, continuing the lling of said vessel substantially to completion to compress the entrapped air and condense the vapors, and venting the entrapped air when thevessel is slightly less than full at a pressure not exceeding the safety limit of the vessel, the venting being continued until the absolute pressure within the vessel above the top of the liquid has fallen to slightly above atmospheric pressure.

2. The method of claim 1 wherein the liquid is introduced into the vessel at such a rate that the pressure of the Volatilized gases Within the vessel is substantially the same as the vapor pressure of thev liquid duringthe lling operation.

3.rv The method of claim 1 wherein the liquid is withdrawn from the vessel at sucha rate that the pressure of the volatilized gases within the vessel is substantially the same, as the vapor pressure of the liquid during the emptying operation.

4. The method of claim 1 wherein the. liquid is introduced into and withdrawn from the vessel at such a rate that the pressure of the volatilized Y gases within the vessel is substantially the same as the Vapor pressure of the liquid. during the nlling and emptying operations.

5. A storage system for storing volatile liquids having a substantial vapor pressure substantially below atmospheric pressure comprising a storage vessel capable of withstanding substantially a full vacuum and also an internal gauge pressure substantially equal to atmospheric pressure, a vent connected to the vessel and having a pressure responsive valve closure therein adapted to open in response to the build up in the vessel of an internal pressure slightly less thanthe safety limit of the vessel and to remain open only while said internal pressure is maintained, a second vent connected to the vessel and having a pressure responsive valve closure therein adapted to open in response to the build up in the'vessel of u an internal pressure slightly less than the safety REFERENCES CTEB The following references are of recordin the iileof thisv patent:

UNITED STATES PATENTS Number Name Date 1,666,935 Howell Apr. 24, 1928 1,890,870 Tokheim Dec. 13, 1932 2,037,731 Mobley Apr. 21, 193.6 2,313,997 Jackson Mar. 16, 1943 2,333,792 Jackson Nov. 9, 1943 2,376,263`

Marner May l5, 1945 

